The purpose of this investigation is to identify and characterize deficits in response maintenance and switching in adults with idiopathic Parkinson's disease (IPD), and to determine how these deficits change with withdrawal of dopaminergic medications. IPD is traditionally viewed as a disorder of motor control that affects the execution of movement. However, arguments for additional disruption during response preparation derive from research on limb movement disorders (Gentilucci & Negrotti, 1999), neuroimaging (Deiber et al., 1996) and neuropsychology (Ravizza & Ciranni, 2002). Converging evidence suggests that prior to movement people with IPD have reduced ability to maintain a prepared response (Gueye et al., 1998) or to switch from a prepared response to a novel response (Roy et al., 1993). To date, the potential influence of these preparatory deficits on the speech of people with IPD has been largely ignored (Spencer & Rogers, in press). Many questions remain unanswered regarding the presence/nature of these deficits during speech preparation, the relationship preparatory deficits may have to the dysarthria of IPD, and the role of dopamine in the manifestation of these preparatory deficits. Priming paradigms can be designed to evaluate response preparation (Yaniv et al., 1990). Two response priming paradigms will be used to begin to characterize the nature of the observed response preparation deficits. One paradigm has increased speech motor programming demands while the second paradigm has increased cognitive demands and decreased motor programming requirements. The first specific aim is to establish response priming patterns across both paradigms for a large group of healthy older adults. It is hypothesized that control participants will exhibit the typically robust reaction time patterns across protocols and experimental conditions. The second specific aim is to determine if priming patterns consistent with aberrant switching and maintenance exist for optimally medicated participants with IPD. Associations are predicted between the presence of dysarthria and abnormal speech priming patterns. The final specific aim is to test the hypothesis that withdrawal of dopaminergic medications will affect the ability to maintain a prepared response or to switch from a prepared response. It is expected that dopamine depletion will have a greater detrimental effect on cognitive versus speech preparatory processes. The proposed investigation would uniquely contribute to theoretical models of response "maintenance" and "switching" in IPD as these functions will be examined across modalities. Clinically, this investigation will offer novel contributions to a sparse literature on the effects of dopaminergic medication on speech planning and production in IPD. [unreadable] [unreadable] [unreadable]